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# Grade 8 waves

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• All of these examplesCANNOT move through empty space.
• Compressional
• The highest point of a transverse wave is the crest and the lowest point is called a trough.
• Compressional
• CompressionalThe place on the wave that is pushed together is called the compression and the place that is moving apart is the rarefaction.
• The wave bends because as it enters a new medium it either speeds up or slows down!
• The wave bends because as it enters a new medium it either speeds up or slows down!
• The wave bends because as it enters a new medium it either speeds up or slows down!
• Refraction and diffraction both cause bending, but refraction occurs when waves move through something, while diffraction occurs when waves pass around something.
• ### Transcript of "Grade 8 waves"

1. 1. Waves Definition, behavior, and classification
2. 2. What’s the underlying theme?
3. 3. What is a wave? A WAVE is a vibration or disturbance in space.
4. 4. What is a wave? Waves transfer energy without transferring matter.
5. 5. How are waves classified? Waves can be classified by WHAT they move through or by HOW particles move through them.
6. 6. What material do waves move through? A MEDIUM is the substance that waves travel through and need to have in order to move.
7. 7. Classification of Waves According to what they move through (Medium) • Electromagnetic waves • Mechanical Waves
8. 8. Electromagnetic Waves • waves that can travel through matter or empty space where matter is not present.
9. 9. • radio waves • microwaves • infrared waves • visible light • ultraviolet rays • X-rays Electromagnetic Waves
10. 10. Mechanical Waves • Needs a medium • require the particles of the medium to vibrate in order for energy to be transferred.
11. 11. • water waves • earthquake/seismic waves • sound waves • waves that travel down a rope or spring Mechanical Waves
12. 12. Classification of Waves According to how particles move through them • Transverse waves • Longitudinal Waves
13. 13. Transverse Waves Displaces particles perpendicular to the motion of the wave
14. 14. science.hq.nasa.gov/kids/imagers/ems/waves3.html
15. 15. Longitudinal Waves Cause the particles of a medium to move parallel to the direction of motion of the wave.
16. 16. Longitudinal Waves Has a crowded area causing a high- pressure region called compression, and the opposite is rarefaction
17. 17. http://www.lcse.umn.edu/specs/labs/glossary_items/rarefaction_spring.html
18. 18. Transverse and Longitudinal Wave Which is which?
19. 19. Wave Characteristics Wavelength (λ) The distance from crest to crest (or trough to trough); expressed in meters
20. 20. Wave Characteristics Amplitude (A) The distance of crest (or trough) from the midpoint of the wave
21. 21. Wave Characteristics Frequency (f) The number of waves that passed a fixed point per second; measured in hertz (Hz)
22. 22. Periodic Wave Characteristics Period (T) The time it takes a wave to travel a distance equal to a wavelength; measured in second T= 1/f
23. 23. Periodic Wave Characteristics Period (T) start end
24. 24. Period (T) start end
25. 25. Period (T) endstart
26. 26. Periodic Wave Characteristics Wave velocity (v) Distance travelled by a wave crest in one period v= λ/T
27. 27. Wave Behavior What happens when… • A wave meets a hard surface like a wall? • A wave enters a new medium? • A wave moves around an obstacle? • A wave meets another wave?
28. 28. Reflection • When a wave hits a surface through which it cannot pass, it bounces back. • All types of waves can be reflected.
29. 29. Reflection • When a wave hits a surface through which it cannot pass, it bounces back. • All types of waves can be reflected.
30. 30. Reflection Reflection does not change the speed or frequency of the wave, BUT the wave can be flipped upside down!
31. 31. Refraction • The bending of a wave as it enters a new medium. • It is caused by a change in the speed of the wave as it moves from one medium to another – Greater change in speed = more bending of the wave
32. 32. Refraction
33. 33. Refraction
34. 34. Diffraction The bending of a wave as it moves around an obstacle or passes through a narrow opening.
35. 35. Diffraction • The scattering of a wave as it hits the edges of a boundary or tiny opening. • The wave will try to curve around the boundary or outward through the opening.
36. 36. Refraction vs. Diffraction • Both cause bending, but refraction occurs when waves move through something, while diffraction occurs when waves pass around something.
37. 37. Interference When two or more waves are moving through a medium at the same time, they may overlap or combine together.
38. 38. Interference
39. 39. Constructive Interference When two waves combine to make a wave with larger displacement or amplitude. –“Helping each other”
40. 40. Destructive Interference • Two or more waves combine to produce a wave with a smaller displacement.
41. 41. Problem Solving Time!  1. A wave in a spring has a wavelength of 0.1 meters and a period of 0.2 seconds. What is the speed of the wave? • v= λ/T • v = 0.1 m / 0.2 s • v = 0.5 m/s
42. 42. Problem Solving Time!  2. Find the wavelength of a wave in a rope that has a frequency of 2.0 Hz and a speed of 0.4 meters/second. • v= λ/T; T = 1/f • λ = v / f • λ = 0.4 m/s / 2.0 Hz • λ = 0.2 m
43. 43. 0 cm 5 -10 -5 10 3. What is the amplitude of the wave? Amplitude = 5cm
44. 44. Problem Solving Time!  4. A hiker shouts on top of a mountain toward a vertical cliff, 688m away. The echo is heard 4s after. a. What is the speed of sound? b. The wavelength of the sound is 0.75m. What is its frequency? c. What is the period of the wave?
45. 45. Problem Solving Time!  a)Speed v = d/t v = 688m/2s v = 344m/s2 s 2 s 4 seconds
46. 46. Problem Solving Time!  b) Frequency v = λ/T; f = v/λ f = 344m/s / 0.75m f = 458.67 Hz 4 seconds
47. 47. Problem Solving Time!  c) Period T = 1/f T = 1/458.67 Hz T = 2.18x10-3s 4 seconds
48. 48. Problem Solving Time!  5. If the frequency of a sound wave is doubled, what happens to the period of the same sound wave? The period will be halved.
49. 49. Problem Solving Time!  6. If the speed of wave is doubled, what happens to the frequency of the same wave if the wavelength is constant? The frequency will be doubled.
50. 50. Problem Solving Time!  6. If the speed of wave is doubled, what happens to the frequency of the same wave if the wavelength is constant? The frequency will be doubled.
51. 51. Problem Solving Time!  7. If the wavelength is halved and the frequency is quadrupled, what will be the speed of the wave? (in multiples of v) 2V.
52. 52. Problem Solving Time!  C F E A B D
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